1. Field of the Invention
The present invention generally relates to a spine formation device to form a spine of a bundle of folded sheets, a bookbinding system including the spine formation device and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine capable of at least two of these functions, and a spine formation method.
2. Description of the Background Art
At present, saddle-stitching or saddle-stapling, that is, stitching or stapling a bundle of sheets along its centerline is widely used as a simple bookbinding method. Typically, the spine of the bundle of sheets (hereinafter “a booklet”) produced through saddle-stitching bookbinding tends to bulge as a result of being folded along its centerline. It is preferred to reduce such bulging of the spine of the booklet, that is, to flatten the spine of the booklet, to improve its appearance and to facilitate stacking, storage, and transport of the booklet.
More specifically, when a bundle of sheets is saddle-stitched or saddle-stapled and then folded in two, the folded portion around its spine tends to bulge, degrading the overall appearance of the booklet. In addition, because the bulging spine makes the booklet thicker on the spine side and thinner on the opposite side, when the booklets are piled together with the bulging spines on the same side, the piled booklets tilt more as the number of the booklets increases. Consequently, the booklets might fall over when piled together.
By contrast, when the spine of the booklet is flattened, bulging of the booklet can be reduced, and accordingly multiple booklets can be piled together. This flattening is important for ease of storage and transport because it is difficult to stack booklets together if their spines bulge, making it difficult to store or carry them. With this reformation, relatively large number of booklets can be piled together. It is to be noted that the term “spine” used herein means not only the stitched side of the booklet but also portions of the front cover and the back cover continuous with the spine.
In view of the foregoing, for example, the following approaches have been proposed to flatten the spine of the booklet.
For example, in JP-2001-260564-A, the spine of the booklet is flattened using a pressing member configured to clamp an end portion of the booklet adjacent to the spine and a spine-forming roller configured to roll on longitudinally while contacting the spine of the booklet. The spine-forming roller moves at least once over the entire length of the spine of the booklet fixed in place by the pressing member while applying to the spine a pressure sufficient to flatten the spine.
Although this approach can flatten the spine of the booklet to a certain extent, it is possible that the sheets might wrinkle and be torn around the spine or folded portion because the pressure roller applies localized pressure to the spine continuously. Further, it takes longer to flatten the spine because the pressure roller must move over the entire length of the spine of the booklet.
Therefore, for example, in JP-2007-237562-A, the spine of the booklet is flattened using a spine pressing plate pressed against the spine of the booklet, a clamping member that clamps the bundle of folded sheets from the front side and the back side of the booklet, and a pressure member to squeeze the spine from opposing sides of the booklet in the direction of the thickness of the booklet to reduce bulging of the spine.
However, because only the bulging portion is pressed with the spine-forming roller in the first approach, the booklet can wrinkle in a direction perpendicular to the longitudinal direction in which the spine extends, degrading its appearance. In addition, with larger sheet sizes, productivity decreases because it takes longer for the spine-forming roller to move over the entire length of the spine of the booklet. At present, it is important to operate such spine formation devices efficiently to reduce energy consumption. Generally, when efficiency is considered, processing conditions such as the degree of pressure and the number of repetitions vary depending on the quantity of sheets, sheet thickness, and sheet type. However, in the first approach using the spine-forming roller, only the number of times the spine-forming roller moves the entire length of the spine of the booklet can be adjusted, and thus it is difficult to make processing more efficient.
In addition, although the second approach can reduce the occurrence of wrinkles in and damage to the booklet caused by the first method described above, the processing time can still be relatively long because the clamping member, the pressure member, and so forth are all operated consecutively and not simultaneously after the booklet is pressed against the spine pressing plate.
In addition, the device according to the second approach described above is bulky because a motor is necessary to move the spine pressing plate in a reverse direction of the sheet conveyance direction. Moreover, a relatively large driving force is necessary because the bulging is formed by pressing the booklet a relatively short distance between the spine pressing plate and the clamping member with the spine pressing plate, increasing the power consumption, which is not desirable.
In view of the foregoing, the inventors of the present invention recognize that there is a need to reliably reduce bulging of booklets, regardless of the thickness of the booklet or the number of sheets, while reducing damage to the booklet, which known approaches fail to do.